Light diffusion device

ABSTRACT

A light diffusion device comprising a transparent resin film having a coating adhered to one surface thereof and comprising the solid contents of a resin lacquer composition containing particulated alumina dispersed therein. A preferred embodiment comprises the use of a saturated polyester resin, both for said film and said lacquer.

United States Patent Hoffman et a1.

[54] LIGHT DIFFUSION DEVICE [72] Inventors: Mark Hoffman; Claude AlanLindquist, Jr., both of 253 E. 42nd Street, New York, NY. 10017 [22]Filed: Apr. 20, 1970 [21] Appl.No.: 30,272

[52] U.S.Cl ..350/1 26, 117/33.3, 117/76 F, 117/l38.8 F,117/138.8UA,117/138.8 G, 117/161 K, 161/35 [51] Int. Cl. ..G03b 21/60 [58] FieldofSearch ..117/138.8 F, 138.8 A, 33.5 T, 117/33.5 R, 33.3, 76 F,73,159;350/188, 126; 161/35 [56] References Cited UNITED STATES PATENTS3,351,409 11/1967 McGuire ..117/33.3X

[15] 3,655,263 [451 Apr.11,.1972

2,878,136 3/1959 Gustin ..1 17/33.5 R X 2,878,137 3/1959 Butler etal.... 17/33.5 R X 2,362,980 ll/l944 Ball ..l l7/l5 X 2,892,747 6/1959Dye 161/214 3,491,237 l/1970 Tillett ..350/l 88 Primary Examiner-WilliamD. Martin Assistant Examiner-Ralph Husack Attorney-Connolly and Hutz 57] ABSTRACT 6 Claims, No Drawings LIGHT DIFFUSION DEVICE BACKGROUND OFTHE INVENTION The present invention relates to a device or medium fordiffusing light. Such diffusers may be used for lighting of all kindsbut are of particular importance in the photographic and otherreprographic fields. The diffusers of the instant invention areadmirably suited for rear projection screens for a number of reasons.For example, the projected light is sufficiently diffused to avoid hotspot, the projected colors are lifelike, i.e., are not significantlymodified by the screen, the brightness of the image on the screen viewedat angles other than is excellent as compared to commercially availablerear projection screens and the projected image is of non-granularappearance. Although a number of prior art screens have offered some ofthe above advantages, none have embodied all of them.

SUMMARY OF THE INVENTION The diffusion device of the present inventioncomprises a transparent resin film having front and rear surfaces and arelatively thin coating adhered to one of said surfaces and comprisingthe solids content of a resin lacquer composition containing dispersedtherein particulated alumina having an average particle diameter rangingfrom about 0.25 to 40 microns, the ratio by weight of said alumina tosaid resin in said lacquer being from about 0.5:1 to 3:1 and thepercentage difference of the indices of refractions of the resin of saidfilm and of said alumina being from 1 to 25 percent. A modified form ofthe present invention includes a protective coating of a clear,transparent resin applied to the surface of said lacquer coating.Although the diffusion device of the present invention may be used for aplurality of purposes wherein light diffusion is of importance, it isparticularly adapted for rear projection screens, i.e., screens whereinan image is projected on one side by a projection device such as a movieprojector and the resulting image is viewed from the other side. Theinstant diffusers are also suitable as front projection screens.

DETAILED DESCRIPTION OF THE INVENTION The transparent resin filmcomponent of the diffuser of the instant invention may be produced froma variety of resins. It is only necessary that the resin be atransparent film forming resin having an index of refraction of a valuesuch that the percentage difference of the indices of refractions of theresin of the film and of the alumina component is from 1 to 25 percent,preferably about 5 to about percent. Index of refraction as referred toherein is the value obtained employing A.S.T.M. Test Method D542. Thefollowing is a tabulation of exemplary resins possessing the transparentfilm-forming capacity together with an index of refraction suitable forestablishing a value within the aforesaid percentage difference range,alumina having a refractive index of 1.764:

Of the aforesaid typical transparent resins, the preferred filmcomponent of the instant invention is based on a saturated polyesterresin, i.e., the product of reaction of a dihydric alcohol and a dibasicacid under controlled conditions wherein water is evolved and chainmolecules having terminal hydroxyl or carboxyl groups result. Aparticularly preferred polyester resin comprises a polymerized linearester of terephthalic acid and ethylene glycol such as described in U.S.Pat. No. 2,465,319.

The resin of the lacquer coating component of the instant invention maycomprise the same resin as that employed in the resin film component oranother resin. It is only necessary that it act as a binder for thealumina thereof and adhere to the resin film surface. Preferably, itcomprises a saturated polyester resin and this is used in conjunctionwith a transparent film of a saturated polyester resin. The preferredpolyester resin lacquer coating component comprises a linear copolymerof a polymethylene glycol containing from two to six carbon atoms,terephthalic acid, isophthalic acid and at least two acyclicdicarboxylic acids, such as described in U.S. Pat. No. 2,892,747.

-The particulated alumina component of the resin lacquer compositionused in the preparation of the diffusion device of the instant inventionpreferably has an average particle diameter from about 0.25 to 40microns. The particularly preferred diameter ranges from about 1 toabout 10 microns. The ratio by weight of the alumina to resin in thelacquer should range from about 0.5:] to 3:1.

A variety of solvents such as dioxane, tetrahydrofuran, methylenechloride, chloroform, etc., may be employed for the purpose of preparingthe lacquer coating compositions used in the preparation of thediffusion devices of the instant invention. The amount employed isdetermined by the consistency of the lacquer desired for the particularselected coating technique. As shown by the working examples appearinghereinafter, various additives such as conventional curing agents,antistatic agents, etc. may be included in the lacquer.

The resin film of the present invention is preferably self-supporting.In general, a film thickness ranging from about 0.001 to about 0.1 inchthick provides a preferred diffusion device when used in conjunctionwith an alumina containing coating having a thickness from about 0.0001to about 0.0009 inch. 1n the embodiment including a clear, transparentresin protective coating on the alumina containing coating, a protectivecoating thickness of from about 0.0001 to about 0.0005 inch ispreferred.

The following examples illustrate preparation of preferred embodimentsof the diffusion device of the instant invention.

EXAMPLE 1 A1 0 having an average particle diameter of about 5 microns2367 g. Lacquer resin (25% solids) 3672 g. Sodium dioctyl sulfosuccinate27 g. Lecithin 72 g. Polyisocyanate curing agent 67.5 g. Dioxane 306 g.

The foregoing ingredients except for the curing agent and dioxane wereplaced in a four gallon alumina-fortified pebble mill containingone-half its volume of inch high density (high alumina) grinding mediaand the mill was operated for 16 hours. Thereafter, the curing agent andsolvent were added and the mill was operated for an additional 30minutes to provide the alumina containing lacquer.

The aforesaid polyester resin of the alumina containing lacquer was ofthe type described in U.S. Pat. No. 2,892,747, Example 1 thereof being apreferred embodiment. The

polyisocyanate curing agent was of the type described in US. Pat. No.2,683,730, Example ll thereof being a preferred embodiment.

EXAMPLE 2 The procedure of Example 1 was repeated employing thefollowing alumina containing lacquer composition:

Al,0, having an average particle diameter of about 5 microns 394 g.Lacquer resin (25% solids) 1224 g. Sodium dioctyl sulfosuccinate 9 g.Lecithin 24 g. Polyisocyanate curing agent 37 g. Dioxane of a saturatedpolyester resin lacquer composition containing dispersed thereinparticulated alumina having an average particle diameter ranging fromabout 0.25 to 40 microns, the ratio by weight of said alumina to saidresin in said lacquer being from about 0.5:1 to 3:1 and the percentagedifference of the indices of refractions of the resin of said film andof said alumina being from 1 to 25 percent.

2. The diffusion device of claim 1 wherein said film is about 0.001 toabout 0.1 inch thick.

3. The diffusion device of claim 1 wherein said coating has appliedthereto a protective coating of a clear, transparent resin.

4. The diffusion device of claim 1 wherein said percentage difference isfrom about 5 to about 10 percent.

5. The diffusion device of claim 1 wherein said resin film is asaturated polyester resin.

6. The diffusion device of claim 5 wherein said resin of said film is apolymerized linear ester of terephthalic acid and ethylene glycol andsaid polyester resin of said lacquer composition is a linear copolymerof a polymethylene glycol containing two to six carbon atoms,terephthalic acid, isophthalic acid and at least two acyclicdicarboxylic acids.

* gge I I 516M STATES PATEi lT OFFICE CERTIFICATE 'OF CORRECTIQN 3, 5563 a Dated April 11, 1 2

Patent No.

Mark Hoffman and Claude Alan Lindquist -Inventor(s) It is certified thaterror appears in the above identified patent and that said LettersPatent are hereby corrected as shown below:

- Format page, column 1, after data element "[72] 1 should readInventers: Mark Hoffman of Phillipsburg,

New Jersey; Claude Alan Lindquist of Easton, Pennsylvania between dataelements [72] and [-22] should read [73] Assignee: Pfizer Inc., New YorkSigned and sealed this 29th day of August 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner 0f Patents EDWARD M.FLETCHER,JR.Attesting Officer 7' MIIIEITEE STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,655,263 Dated April 97 Mark Hoffman and ClaudeAlan Lindquist Inventor(s) It is certified that error appears in theabove identified patent and that said Letters Patent are herebycorrected as shown below:

I I I Format page, column 1, after data element "[72]" I should readInventors: Mark Hoffman of Phillipsburg, I

New Jersey; Claude Alan Lindquist of Easton, Pennsylvania between dataelements [72] find [22] should read [73] Assignee: Pfizer 'Inc., NewYork,

Signed and sealed this 29th day of August 1972 (SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patent:

EDWARD M.FLETCHER,JR. Attesting Officer

2. The diffusion device of claim 1 wherein said film is about 0.001 toabout 0.1 inch thick.
 3. The diffusion device of claim 1 wherein saidcoating has applied thereto a protective coating of a clear, transparentresin.
 4. The diffusion device of claim 1 wherein said percentagedifference is from about 5 to about 10 percent.
 5. The diffusion deviceof claim 1 wherein said resin film is a saturated polyester resin. 6.The diffusion device of claim 5 wherein said resin of said film is apolymerized linear ester of terephthalic acid and ethylene glycol andsaid polyester resin of said lacquer composition is a linear copolymerof a polymethylene glycol containing two to six carbon atoms,terephthalic acid, isophthalic acid and at least two acyclicdicarboxylic acids.